This invention relates to an electrode for use in metal electrowinning and electrorefining processes and more particularly, to a stationary particulate bed dual electrode.
In conventional electrowinning and electrorefining processes for recovering metal values from liquid solutions, the electrodes have assumed the form of flat plates onto which the metals deposit when an electrical potential is maintained between an anode and a cathode submerged in the solution. With flat plate electrodes, however, the solution must be highly electrically conductive and highly concentrated in the metallic ion whose deposition is desired. This is so because the rate of transfer of the ion species frame solution to the surface of the electrode depends both on the conductivity of the solution and the electrode surface area available for the deposition reaction. With flat plate electrodes, the surface area available for the deposition reaction is necessarily limited.
In copper electrowinning using flat plate electrodes, for example, effective operation requires a highly electrically conductive solution containing at least 30 to 45 grams/liter of copper ions. Furthermore, a conventional, flat plate electrode electrowinning process is capable of reducing the concentration of copper from 45 grams/liter in a feed solution, for example, to only about 30 grams/liter in the effluent on a single pass through the electrowinning cell.
Electrowinning electrodes employing porous or particulate conductive media to enhance the surface area for metal deposition are known. The handling of such electrodes in commercial installations can be cumbersome and highly labor intensive because of the large numbers of electrodes involved in a typical tankhouse operation and the measure necessary to keep each electrode functioning properly. For example, a particulate bed electrode first must be loaded with fresh or recycled conductive particules or other porous media. After metal deposition upon the particulate medium has been completed, the electrode must be removed from the electrowinning cell and disassembled so that the particulates containing the metal product can be unloaded and transferred in bulk to the next processing stage.
The unloading of the metal containing particulates is particularly difficult in situations in which metallic dendrites grow beyond the boundaries of the particulate bed and through the supporting interface material, creating thereby a bond between the interface material and the metal-laden particulates. This bonding necessarily makes it difficult and time consuming to unload the metal-particulate aggregate.
Another difficulty can be the distortion of the electric field by the supporting interface material, causing non-uniformity in the rate of metal deposition and even creating blind, or unreactive, areas in the particulate bed through which the metal containing solution may pass unaltered, degrading the metal removing efficiency of the cell.
It is, therefore, one object of this invention to provide a low cost, highly efficient stationary particulate bed dual electrode design capable of recovering metal values from dilute, poorly electrically conductive solutions, with minimum downtime.
Another object of the invention is the development of such an electrode for use in conventional tankhouse facilities which is easily removed, readily disassembled for removal of the metal laden particles and quickly reassembled for refilling with fresh conductive particles.
Yet another object is to provide an electrowinning electrode which eliminates bonding of the metal laden particles with the supporting interface material thereby assuring ease of aggregate removal, and which minimizes unreactive or blind areas through which the metal-containing solution may pass unchanged.
Other objects, features and advantages of the present invention will become apparent in what follows.